Vehicle driving support device

ABSTRACT

A vehicle driving support device issues an alert to notify a driver of a vehicle that there is a possibility of occurrence of a situation in which the vehicle is not able to travel along a lane. The vehicle driving support device issues an alert when an alert condition that a rate of increase in a lateral acceleration of the vehicle is equal to or larger than a predetermined rate of increase is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/403,184, filed on Aug. 16, 2021, in U.S. Patentand Trademark Office, which claims priority to Japanese PatentApplication No. 2020-192330, filed on Nov. 19, 2020, in the Japan PatentOffice, the disclosures of which are incorporated by reference herein intheir entireties.

BACKGROUND 1. Technical Field

The present disclosure relates to a vehicle driving support device.

2. Description of Related Art

A vehicle driving support device is known that issues an alert to notifya driver of a vehicle that the vehicle cannot travel along the lane. Asthe vehicle driving support device mentioned above, a vehicle drivingsupport device is also known (see Japanese Unexamined Patent ApplicationPublication No. 2002-79895 (JP 2002-79895 A), for example). The vehicledriving support device acquires by calculation the yaw rate of thevehicle required to be generated (required yaw rate) at that moment inorder for the vehicle to reach the center point of the lane that is apredetermined distance forward of the vehicle. When a deviation of thecurrent actual yaw rate from the required yaw rate is large, the vehicledriving support device determines that the vehicle cannot travel alongthe lane and issues an alert.

SUMMARY

The related-art vehicle driving support device mentioned above issues analert when the deviation between the required yaw rate and the currentactual yaw rate is large. Therefore, the alert is issued after thevehicle actually stops following the lane. However, there is a certainbenefit in predicting that the vehicle will stop following the lane andnotifying the driver of this with an alert before the vehicle actuallystops following the lane.

An object of the present disclosure is to provide a vehicle drivingsupport device capable of notifying a driver that there is a possibilityof occurrence of a situation in which a vehicle is not able to travelalong a lane.

A vehicle driving support device according to the present disclosureincludes a control unit that issues an alert to notify a driver of avehicle that there is a possibility of occurrence of a situation inwhich the vehicle is not able to travel along a lane. The control unitis configured to issue the alert when an alert condition that a rate ofincrease in a lateral acceleration of the vehicle is equal to or largerthan a predetermined rate of increase is satisfied.

The vehicle driving support device according to the present disclosureuses the rate of increase in the lateral acceleration to determinewhether to issue an alert. Therefore, it can be predicted that there isa possibility of occurrence of a situation in which the vehicle is goingto travel on the road where a large lateral acceleration is generatedand the vehicle is not be able to travel along the lane unless a largesteering force is applied to the vehicle. When such a prediction ismade, the alert is issued, so it is possible to notify the driver thatthere is a possibility of occurrence of a situation in which the vehicleis not able to travel along the lane.

In the vehicle driving support device according to the presentdisclosure, the control unit may be configured to set a level of thealert to be lower when a steering wheel operation by the driver isdetected than when the steering wheel operation by the driver is notdetected.

For example, when the driver is operating the steering wheel bythemselves when the alert condition is satisfied, the driver must steerthe vehicle by themselves such that the vehicle travels along the lanewhen the vehicle travels on the road where a large lateral accelerationis generated. In this case, issuing an alert may make the driver feelannoyed. In contrast, if the driver is not operating the steering wheelwhile looking aside, taking a nap, or taking their hands off thesteering wheel, the alert is useful to the driver.

The vehicle driving support device according to the present disclosuresets the alert level to be lower when the steering wheel operation bythe driver is detected than when the steering wheel operation by thedriver is not detected. Thus, when the alert may make the driver feelannoyed, a low level alert is issued, and when issuing the alert isuseful for the driver, a high level alert is issued. Therefore, it ispossible to issue a useful alert while suppressing making the driverfeel annoyed.

The alert condition may include a condition that a steering wheeloperation by the driver is not detected. With this, when the steeringwheel operation by the driver is detected, the alert is not issued.Thus, it is possible to issue a useful alert while suppressing makingthe driver feel annoyed.

The alert condition may include a condition that the lateralacceleration is equal to or larger than a predetermined lateralacceleration. This allows the alert to be issued only when the lateralacceleration is large and the rate of increase in the lateralacceleration is also large at that time and therefore a situation islikely to occur in which the vehicle is not able to travel along thelane.

The constituent elements of the present disclosure are not limited tothe embodiment of the present disclosure described later with referenceto the drawings. Other objects, other features and accompanyingadvantages of the present disclosure will be readily understood from thedescription of the embodiment of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a diagram showing a vehicle driving support device accordingto an embodiment of the present disclosure and a vehicle equipped withthe vehicle driving support device;

FIG. 2 is a diagram showing a road on which the vehicle equipped withthe vehicle driving support device according to the embodiment of thepresent disclosure travels, and the like;

FIG. 3 is a time chart showing a lateral acceleration increase rate andthe like when the vehicle equipped with the vehicle driving supportdevice according to the embodiment of the present disclosure travels onthe road shown in FIG. 2 ;

FIG. 4 is a flowchart showing a routine executed by the vehicle drivingsupport device according to the embodiment of the present disclosure;and

FIG. 5 is a flowchart showing a routine executed by the vehicle drivingsupport device according to a modification of the embodiment of thepresent disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a vehicle driving support device according to an embodimentof the present disclosure will be described with reference to thedrawings. FIG. 1 shows a vehicle driving support device 10 according tothe embodiment of the present disclosure and a vehicle 100 equipped withthe vehicle driving support device 10.

ECU

The vehicle driving support device 10 includes an electronic controlunit (ECU) 90. The ECU is an abbreviation for electronic control unit.The ECU 90 includes a microcomputer as a main component. Themicrocomputer includes a central processing unit (CPU), a read onlymemory (ROM), a random access memory (RAM), a non-volatile memory, aninterface, and the like. The CPU realizes various functions by executinginstructions, programs, or routines stored in the ROM.

Forward Information Providing Device, Etc.

The vehicle 100 is equipped with a steering device 11, a steering anglesensor 21, a steering torque sensor 22, a vehicle speed sensor 23, alane keeping support operation unit 24, a forward information providingdevice 25, a Global Positioning System (GPS) device 26, and an alertdevice 27.

Steering Device

The steering device 11 is a device that outputs a steering force(steering torque) applied to the vehicle 100 to steer the vehicle 100,and is, for example, a power steering device. The steering device 11 iselectrically connected to the ECU 90. The ECU 90 can control thesteering force output from the steering device 11 by controlling theoperation of the steering device 11.

Steering Angle Sensor and Steering Torque Sensor

The steering angle sensor 21 is a sensor that detects a rotation angleof a steering wheel 31 (or a steering shaft 32) with respect to theneutral position. The steering angle sensor 21 is electrically connectedto the ECU 90. The steering angle sensor 21 transmits information on thedetected rotation angle of the steering wheel 31 to the ECU 90. The ECU90 acquires the rotation angle of the steering wheel 31 as a steeringangle θ based on the information.

The steering torque sensor 22 is a sensor that detects the torque inputto the steering shaft 32 via the steering wheel 31. The steering torquesensor 22 is electrically connected to the ECU 90. The steering torquesensor 22 transmits information of the detected torque to the ECU 90.Based on the information, the ECU 90 acquires the torque input to thesteering shaft 32 via the steering wheel 31 as a steering torque TQ.

The ECU 90 acquires by calculation a required steering force (requiredsteering torque) from the steering angle θ and the steering torque TQ.Alternatively, the ECU 90 corrects the calculated required steeringforce as necessary to acquire a corrected required steering force(corrected required steering torque) while a lane keeping supportcontrol described later is being executed. The required steering forceand the corrected required steering force are steering forces for whichoutput is required of the steering device 11. The ECU 90 controls theoperation of the steering device 11 so that the required steering forceor the corrected required steering force is output. Further, the ECU 90can determine whether the operation of the steering wheel 31 by thedriver (steering wheel operation of the driver) is being performed, fromthe steering angle θ, the steering torque TQ, and the like.

Vehicle Speed Sensor

The vehicle speed sensor 23 is a device that detects the vehicle speedof the vehicle 100, and has, for example, a wheel speed sensor. Thevehicle speed sensor 23 is electrically connected to the ECU 90. Thevehicle speed sensor 23 transmits information on the detected vehiclespeed of the vehicle 100 to the ECU 90. The ECU 90 acquires the vehiclespeed of the vehicle 100 as a vehicle speed Vown based on theinformation.

Lane Keeping Support Operation Unit

The lane keeping support operation unit 24 is a device operated by thedriver of the vehicle 100 in order to request the execution of the lanekeeping support control described later as the vehicle driving supportcontrol, and has at least one of a button, a switch, and the like, forexample. The lane keeping support operation unit 24 is electricallyconnected to the ECU 90. When a predetermined operation requestingexecution of the lane keeping support control is performed, the lanekeeping support operation unit 24 transmits a signal corresponding tothe predetermined operation to the ECU 90. When the ECU 90 receives thesignal, the ECU 90 determines that the execution of the lane keepingsupport control is requested.

Forward Information Providing Device

The forward information providing device 25 is a device that providesinformation forward of the vehicle 100, and has at least one of “asensor such as a camera, a radar sensor (millimeter wave radar, and thelike), an ultrasonic sensor (clearance sonar), and a laser radar (lightdetection and ranging (LiDAR))” and “a road shape database such as a mapdatabase”, for example.

The forward information providing device 25 is electrically connected tothe ECU 90. The forward information providing device 25 providesinformation forward of the vehicle 100 (forward information) to the ECU90. From the forward information, the ECU 90 acquires the curvature ofthe road on which the vehicle 100 is traveling, more specifically, thecurvature of the road forward of the vehicle 100, as a forward roadcurvature R. In particular, the ECU 90 acquires the curvature of a laneLN (see FIG. 2 ) in which the vehicle 100 is traveling, morespecifically, the curvature of the lane LN forward of the vehicle 100,as the forward road curvature R.

For example, when the forward information providing device 25 has acamera, the forward information is information of an image in front ofthe vehicle 100 captured by the camera. In this case, the ECU 90 detects“a lane marking LM such as a white line provided on the road forward ofthe vehicle 100 (see FIG. 2 )” from the information of the image, andacquires the forward road curvature R from the shape of the detectedlane marking LM. Further, the ECU 90 detects, from the information ofthe image, at least one of objects that take a shape along the roadshape, such as “the trajectory of another vehicle (preceding vehicleand/or vehicle alongside) traveling in front of the vehicle 100 on thesame road as the road on which the vehicle 100 is traveling”, “a guardrail GR installed on the road forward of the vehicle 100 (see FIG. 2 )”,and “an outer wall or a fence of a building BD on the side of the roadforward of the vehicle 100 (see FIG. 2 )”, and acquires the forward roadcurvature R from the detected shape of the object.

When the forward information providing device 25 has a sensor, theforward information is object information such as “time from the timethe sensor emits an electromagnetic wave or a sound wave to the time thesensor receives the reflected wave of the electromagnetic wave or thesound wave from the object” and “the direction in which the sensorreceives the reflected wave of the electromagnetic wave or the soundwave”. From the object information, the ECU 90 detects at least one ofthe objects that take a shape along the road shape, such as “the guardrail GR installed on the road forward of the vehicle 100 (see FIG. 2 )”,and “the outer wall or the fence of the building BD on the side of theroad forward of the vehicle 100 (see FIG. 2 )”, and acquires the forwardroad curvature R from the detected shape of the object.

When the forward information providing device 25 has a road informationdatabase, the forward information is road information stored in the roadinformation database. The ECU 90 acquires the shape of the road forwardof the vehicle 100 from the road information and the current position ofthe vehicle 100, and acquires the forward road curvature R from theshape of the road.

GPS Device

The GPS device 26 is a device that receives so-called GPS signals. TheGPS device 26 is electrically connected to the ECU 90. The GPS device 26transmits the received GPS signal to the ECU 90. The ECU 90 acquires thecurrent position of the vehicle 100 based on the GPS signal.

Alert Device

The alert device 27 is a device that issues an alert to the driver ofthe vehicle 100, and has, for example, at least one of a buzzer, aspeaker, a lamp, a display, a vibration device, and the like. The alertdevice 27 is electrically connected to the ECU 90. When an alertcondition Calert, which will be described later, is satisfied, the ECU90 issues an alert to the driver by operating the alert device 27.

When the alert device 27 has a buzzer, the alert is an output of analert sound from the buzzer. When the alert device 27 has a speaker, thealert is an output of voice (announcement) from the speaker. When thealert device 27 is a lamp, the alert is lighting of the lamp. When thealert device 27 is a display, the alert is an indication of anannouncement image on the display. When the alert device 27 is avibration device, the alert is the vibration of the steering wheel 31 orthe driver's seat by the vibration device.

Outline of Operations of Vehicle Driving Support Device

Next, the outline of the operations of the vehicle driving supportdevice 10 will be described. The vehicle driving support device 10issues an alert to notify the driver of the vehicle 100 that there is apossibility of occurrence of a situation in which the vehicle 100 is notable to travel along the lane LN when the predetermined alert conditionCalert is satisfied.

The vehicle driving support device 10 may issue an alert when the alertcondition Calert is satisfied, in the case where the driver of thevehicle 100 requests issuance of an alert, or regardless of whether thedriver of the vehicle 100 requests issuance of an alert, or regardlessof whether the lane keeping support control is being executed. However,in this example, an alert is issued when the alert condition Calert issatisfied during the execution of the lane keeping support control.

Lane Keeping Support Control

The lane keeping support control is a control of acquiring a centerlineLC of the lane LN in which the vehicle 100 is traveling (see FIG. 2 )from the forward information, correcting the required steering force asnecessary so that the vehicle 100 travels along the centerline LC, andproviding the corrected required steering force to the vehicle 100, tocause the vehicle 100 to travel along the centerline LC of the lane LN.In other words, the lane keeping support control is a control forcausing the vehicle 100 to travel along the lane LN.

When determining that the execution of the lane keeping support controlis requested, the vehicle driving support device 10 starts the lanekeeping support control, and when determining that the execution of thelane keeping support control is no longer requested, the vehicle drivingsupport device 10 ends (stops) the lane keeping support control.

Alert

The vehicle driving support device 10 acquires the rate of increase in alateral acceleration Gy (lateral acceleration increase rate Rgy) duringexecution of the lane keeping support control. In this example, thevehicle driving support device 10 acquires by calculation the lateralacceleration Gy based on the forward road curvature R acquired from theforward information and the vehicle speed Vown of the vehicle 100, butthe lateral acceleration Gy acquired by the vehicle driving supportdevice 10 is not limited to this. For example, when the vehicle 100 isequipped with a lateral acceleration sensor, the vehicle driving supportdevice 10 may acquire the lateral acceleration Gy detected by thelateral acceleration sensor to acquire the lateral acceleration increaserate Rgy based on the lateral acceleration Gy.

When the curvature of the road on which the vehicle 100 is travelingincreases while the state in which the vehicle 100 is traveling alongthe lane LN is maintained, the lateral acceleration increase rate Rgyincreases accordingly. Therefore, a large lateral acceleration increaserate Rgy indicates that the curvature of the road on which the vehicle100 is traveling has increased. Therefore, when the lateral accelerationincrease rate Rgy is large, the lateral acceleration Gy is expected toincrease thereafter. If the lateral acceleration Gy becomes very large,the correction of the required steering force by the lane keepingsupport control may reach the limit, and as a result, a situation mayoccur in which the vehicle 100 is not be able to travel along the laneLN without the steering wheel operation by the driver, even under thelane keeping support control.

Thus, the vehicle driving support device 10 determines that the alertcondition Calert is satisfied when the lateral acceleration increaserate Rgy becomes equal to or larger than a predetermined increase rateRgy_th.

In this example, the vehicle driving support device 10 determines thatthe alert condition Calert is satisfied when the lateral accelerationincrease rate Rgy becomes equal to or larger than the predeterminedincrease rate Rgy_th regardless of whether the driver of the vehicle 100is operating the steering wheel 31. However, the vehicle driving supportdevice 10 may determine that the alert condition Calert is satisfiedwhen the lateral acceleration increase rate Rgy becomes equal to orlarger than the predetermined increase rate Rgy_th while the driver ofthe vehicle 100 is not operating the steering wheel 31.

When the vehicle driving support device 10 determines that the alertcondition Calert is satisfied, the vehicle driving support device 10issues an alert. That is, when the alert condition Calert that thelateral acceleration increase rate Rgy is equal to or larger than thepredetermined increase rate Rgy_th is satisfied, the vehicle drivingsupport device 10 determines that there is a possibility of occurrenceof a situation in which the vehicle 100 is not able to travel along thelane LN, and issues an alert.

Further, the vehicle driving support device 10 may stop the alert whenthe alert condition Calert is no longer satisfied, but in this example,the alert is stopped when the alert condition Calert is no longersatisfied and an alert end condition Cend that an elapsed time T fromthe start of the alert has reached a predetermined time Tth issatisfied.

The operations of the vehicle driving support device 10 will bedescribed with reference to FIGS. 2 and 3 . In the example shown in FIG.2 , the road on which the vehicle 100 travels is a straight road SR witha curvature of the lane LN in which the vehicle 100 travels being zeroup to a point P20. The road on which the vehicle 100 travels becomes acurved road CR1 with the curvature of the lane LN in which the vehicle100 travels being a first curvature R1 at the point P20. Then, at apoint P22, the road on which the vehicle 100 travels becomes a curvedroad CR2 with the curvature of the lane LN in which the vehicle 100travels being a second curvature R2 that is larger than the firstcurvature R1.

As shown in FIG. 3 , the lateral acceleration increase rate Rgy acquiredby the vehicle driving support device 10 is zero before the vehicle 100reaches the point P20 (the point where the straight road SR shifts tothe curved road CR1). When the vehicle 100 reaches the point P20, thelateral acceleration increase rate Rgy becomes a first increase rateRgy_1. At this time, since the first increase rate Rgy_1 is smaller thanthe predetermined increase rate Rgy_th, no alert is issued.

After that, the lateral acceleration increase rate Rgy becomes zero whenthe vehicle 100 reaches a point P21. After that, when the vehicle 100reaches a point P22 (the point where the curved road CR1 shifts to acurved road CR2), the lateral acceleration increase rate Rgy becomes asecond increase rate Rgy_2. At this time, since the second increase rateRgy_2 is larger than the predetermined increase rate Rgy_th, the alertis issued. After that, the alert is continued at least while the lateralacceleration increase rate Rgy is larger than the predetermined increaserate Rgy_th.

In this example, when the vehicle 100 reaches a point P23, the lateralacceleration increase rate Rgy becomes zero. At this point, the alertcondition Calert is no longer satisfied, but the alert is continuedbecause the elapsed time T from the start of the alert is shorter thanthe predetermined time Tth. After that, when the vehicle 100 reaches apoint P24, the elapsed time T from the start of the alert reaches thepredetermined time Tth and the alert end condition Cend is satisfied, sothat the alert is ended.

Effects

The vehicle driving support device 10 uses the lateral accelerationincrease rate Rgy to determine whether to issue an alert. Therefore, itcan be predicted that the vehicle 100 is going to travel on the roadwhere a large lateral acceleration Gy is generated and a large steeringforce needs to be applied to the vehicle 100 in order to cause thevehicle 100 to travel along the lane LN. In other words, it can bepredicted that there is a possibility of occurrence of a situation inwhich the vehicle 100 is not able to travel along the lane LN unless alarge steering force is applied to the vehicle 100. When such aprediction is made, the alert is issued, so it is possible to notify thedriver that there is a possibility of occurrence of a situation in whichthe vehicle 100 is not able to travel along the lane LN.

In the above example, the alert condition Calert is a condition that thelateral acceleration increase rate Rgy is equal to or larger than thepredetermined increase rate Rgy_th. However, the alert condition Calertmay be a condition that the lateral acceleration increase rate Rgy isequal to or larger than the predetermined increase rate Rgy_th and thelateral acceleration Gy is equal to or larger than a predeterminedlateral acceleration Gy_th. This allows the alert to be issued only whenthe lateral acceleration Gy is large and the increase rate Rgy is alsolarge at that time and therefore a situation is likely to occur in whichthe vehicle 100 is not able to travel along the lane LN.

Specific Operations of Vehicle Driving Support Device

Next, the specific operations of the vehicle driving support device 10will be described. The CPU of the ECU 90 of the vehicle driving supportdevice 10 executes the routine shown in FIG. 4 every time apredetermined calculation time has elapsed. Thus, at a predeterminedtiming, the CPU starts the process from step 400 in FIG. 4 , advancesthe process to step 405, and determines whether the lane keeping supportcontrol is being executed.

When the CPU determines “Yes” in step 405, the CPU advances the processto step 410 and acquires the lateral acceleration increase rate Rgy.Next, the CPU advances the process to step 415 and determines whetherthe alert condition Calert is satisfied. Specifically, the CPUdetermines whether the lateral acceleration increase rate Rgy acquiredin step 410 is equal to or larger than the predetermined increase rateRgy_th.

When the CPU determines “Yes” in step 415, the CPU advances the processto step 420. The CPU starts the alert when the alert is not being issuedand continues the alert when the alert is being issued. Thereafter, theCPU advances the process to step 495 and temporarily ends the routine.

When the CPU determines “No” in step 415, the CPU advances the processto step 425 and determines whether the alert is being issued.

When the CPU determines “Yes” in step 425, the CPU advances the processto step 430 and determines whether the elapsed time T from the start ofthe alert is equal to or more than the predetermined time Tth.

When the CPU determines “Yes” in step 430, the CPU advances the processto step 435 and stops the alert. Thereafter, the CPU advances theprocess to step 495 and temporarily ends the routine.

When the CPU determines “No” in step 430, the CPU advances the processto step 440 and continues the alert. Thereafter, the CPU advances theprocess to step 495 and temporarily ends the routine.

When the CPU determines “No” in step 425, the CPU directly advances theprocess to step 495 and temporarily ends the routine.

When the CPU determines “No” in step 405, the CPU advances the processto step 445. The CPU stops the alert when the alert is being issued, andwhen the alert is not being issued, the CPU maintains the state in whichthe alert is not being issued. Thereafter, the CPU advances the processto step 495 and temporarily ends the routine.

The above is the specific operations of the vehicle driving supportdevice 10.

Note that the present disclosure is not limited to the above embodiment,and various modifications can be adopted within the scope of the presentdisclosure.

Modifications

For example, when the driver is operating the steering wheel 31 bythemselves when the alert condition Calert is satisfied, the driver muststeer the vehicle 100 by themselves such that the vehicle 100 travelsalong the lane LN when the vehicle 100 approaches a sharp curved road.In this case, issuing an alert may make the driver feel annoyed. Incontrast, if the driver is not operating the steering wheel 31 whilelooking aside, taking a nap, or taking their hands off the steeringwheel 31, the alert is useful to the driver.

The vehicle driving support device 10 described above issues an alertregardless of whether the driver is operating the steering wheel 31 whenthe alert condition Calert is satisfied. However, the vehicle drivingsupport device 10 may be configured to determine whether to issue analert depending on whether the driver is operating the steering wheel 31when the alert condition Calert is satisfied.

Specifically, the vehicle driving support device 10 according to themodification of the embodiment of the present disclosure determineswhether a steering wheel operation condition Csteer that the driver isoperating the steering wheel 31 (namely, steering wheel operationcondition Csteer that the steering wheel operation of the driver isdetected) is satisfied, when the alert condition Calert is satisfied.

The vehicle driving support device 10 issues an alert when the steeringwheel operation condition Csteer is not satisfied. The vehicle drivingsupport device 10 does not issue an alert when the steering wheeloperation condition Csteer is satisfied. Thus, it can be said that thealert condition Calert according to the modification includes acondition that the lateral acceleration increase rate Rgy is equal to orlarger than the predetermined increase rate Rgy_th and a condition thatthe steering wheel operation of the driver is not detected.

Alternatively, when the steering wheel operation condition Csteer is notsatisfied, the vehicle driving support device 10 issues an alert in aform with a high possibility of being noticed by the driver. In otherwords, the vehicle driving support device 10 issues an alert with a highalert level. For example, when the vehicle driving support device 10issues an alert by outputting an alert sound from the buzzer, thevehicle driving support device 10 issues an alert with a high alertlevel by outputting the alert sound from the buzzer at a relatively highvolume. When the steering wheel operation condition Csteer is satisfied,the vehicle driving support device 10 issues an alert in a form with arelatively low possibility of being noticed by the driver. In otherwords, the vehicle driving support device 10 issues an alert with a lowalert level. For example, when the vehicle driving support device 10issues an alert by outputting an alert sound from the buzzer, thevehicle driving support device 10 issues an alert with a low alert levelby outputting the alert sound from the buzzer at a relatively lowvolume. As described above, the vehicle driving support device 10 mayset the alert level to be lower when the steering wheel operation by thedriver is detected than when the steering wheel operation by the driveris not detected.

Next, the specific operations of the vehicle driving support device 10according to the modification will be described. The CPU of the ECU 90of the vehicle driving support device 10 according to the modificationexecutes the routine shown in FIG. 5 every time a predeterminedcalculation time has elapsed. Thus, at a predetermined timing, the CPUstarts the process from step 500 in FIG. 5 , advances the process tostep 505, and determines whether the lane keeping support control isbeing executed.

When the CPU determines “Yes” in step 505, the CPU advances the processto step 510 and acquires the lateral acceleration increase rate Rgy.Next, the CPU advances the process to step 515 and determines whetherthe alert condition Calert is satisfied. Specifically, the CPUdetermines whether the lateral acceleration increase rate Rgy acquiredin step 510 is equal to or larger than the predetermined increase rateRgy_th.

When the CPU determines “Yes” in step 515, the CPU advances the processto step 520 and determines whether the steering wheel operationcondition Csteer is satisfied.

When the CPU determines “Yes” in step 520, the CPU advances the processto step 525. The CPU stops the alert when the alert is being issued, andwhen the alert is not being issued, the CPU maintains the state in whichthe alert is not being issued. Alternatively, the CPU starts the alertwith a low alert level when the alert with a low alert level is notbeing issued, and continues the alert with a low alert level when thealert with a low alert level is being issued. Thereafter, the CPUadvances the process to step 595 and temporarily ends the routine.

When the CPU determines “No” in step 520, the CPU advances the processto step 530. The CPU starts the alert when the alert is not being issuedand continues the alert when the alert is being issued. Thereafter, theCPU advances the process to step 595 and temporarily ends the routine.

When the CPU determines “No” in step 515, the CPU advances the processto step 535 and determines whether the alert is being issued.

When the CPU determines “Yes” in step 535, the CPU advances the processto step 540 and determines whether the elapsed time T from the start ofthe alert is equal to or more than the predetermined time Tth.

When the CPU determines “Yes” in step 540, the CPU advances the processto step 545 and stops the alert. Thereafter, the CPU advances theprocess to step 595 and temporarily ends the routine.

When the CPU determines “No” in step 540, the CPU advances the processto step 550 and continues the alert. Thereafter, the CPU advances theprocess to step 595 and temporarily ends the routine.

When the CPU determines “No” in step 535, the CPU directly advances theprocess to step 595 and temporarily ends the routine.

When the CPU determines “No” in step 505, the CPU advances the processto step 555. The CPU stops the alert when the alert is being issued, andwhen the alert is not being issued, the CPU maintains the state in whichthe alert is not being issued. Thereafter, the CPU advances the processto step 595 and temporarily ends the routine.

The above is the specific operations of the vehicle driving supportdevice 10 according to the modification.

What is claimed is:
 1. A vehicle driving support device comprising acontrol unit that issues an alert to notify a driver of a vehicle thatthere is a possibility of occurrence of a situation in which the vehicleis not able to travel along a lane, wherein the control unit isconfigured to issue an alert notifying the driver of the vehicle thatthe vehicle is not able to travel along the lane without a steeringwheel operation by the driver, when an alert condition that a rate ofincrease in a lateral acceleration of the vehicle is equal to or largerthan a predetermined rate of increase is satisfied.
 2. The vehicledriving support device according to claim 1, wherein the control unit isfurther configured to: set a level of the alert to a first value when asteering wheel operation by the driver is detected; and set the level ofthe alert to a second value when the steering wheel operation by thedriver is not detected, wherein the first value is less than the secondvalue.
 3. The vehicle driving support device according to claim 1,wherein the alert condition includes a condition that a steering wheeloperation by the driver is not detected.
 4. The vehicle driving supportdevice according to claim 1, wherein the control unit is furtherconfigured to calculate the rate of increase in the lateral accelerationof the vehicle based on forward information obtained from at least oneof a camera, object information, and a road information database.
 5. Avehicle driving support device comprising a control unit that issues analert to notify a driver of a vehicle that there is a possibility ofoccurrence of a situation in which the vehicle is not able to travelalong a lane, wherein the control unit is configured to: determine thatexecution of lane keeping support control is requested when apredetermined operation requesting execution of the lane keeping supportcontrol is performed; and based on a determination that the execution ofthe lane keeping support control is requested, issue an alert notifyingthe driver of the vehicle that the vehicle is not able to travel alongthe lane without a steering wheel operation by the driver, when an alertcondition that a rate of increase in a lateral acceleration of thevehicle is equal to or larger than a predetermined rate of increase issatisfied.
 6. The vehicle driving support device according to claim 5,wherein the control unit is further configured to calculate the rate ofincrease in the lateral acceleration of the vehicle based on forwardinformation obtained from at least one of a camera, object information,and a road information database.